The chemical name of dexmethylphenidate hydrochloride is (2R)-phenyl-[(2R)-piperidyl-2-yl-acetic acid methyl ester hydrochloride and it is also known as d-threo-enantiomer of methylphenidate hydrochloride. Methylphenidate hydrochloride is a mixture of dl-threo racemates and it is prescribed as psychostimulant. Dexmethylphenidate marketed as its hydrochloride salt, under the brand name “Focalin”. Subsequence study of methylphenidate hydrochloride revealed that its two enantiomers i.e. dl-threo methylphenidate hydrochloride and d-threo enantiomers are considered to be active disclosed in Biochemistry Pharmacology 1961, 8, 263-268. It is used in treatment of Attention Deficient Hyperactivity Disorder (ADHD). Further, OPRD 2000, 4, 55-59 mentions that (R,R) enantiomer of methylphenidate (dexmethylphenidate) is about 5 to 38 times more active than its corresponding (S,S) enantiomer of methylphenidate.

U.S. Pat. No. 2,957,880 discloses a process for preparing methylphenidate as a mixture of the erythro [R*, S*] and threo [R*, R*] racemates. Also discloses threo isomer of ritalinic acid prepared from the corresponding acid amide, in which resolution of amide using d-tartaric acid converted to (R,R)-ritalinic acid in three steps.
Another several methods are reported for the resolution of dl-threo-methylphenidate by using expensive resolving agent like 1,1′-binaphthyl-2,2′-diyl hydrogen phosphate. Other resolving agents like O,O-diaroyltartaric acid or menthoxy-acetic acid or dibenzoyl-D-tartaric acid are disclosed in WO09727176, GB97/00643, U.S. Pat. Nos. 6,100,401, 6,121,453, 6,162,919 and 6,242,464 for the resolution of dl-threo-methylphenidate. Resolution of threo-methylphenidate may also be achieved by enzymatic hydrolysis methods proposed by Prashad (1998) [U.S. Pat. No. 7,247,730] and in WO98/25902. The main drawbacks of the above cited processes are resolution at the final stage may leads to poor enantiomeric purity and further need to be purified. The additional steps of purification may make the process expensive and tedious. In addition, the enzymatic hydrolysis is time consuming process and may affect the fast output of the product.
U.S. Pat. No. 6,441,178 discloses the resolution of dl-threo-ritalinic acid salt. The resolution performed by treating dl-threo-ritalinic acid hydrochloride with (−)-1-phenylethylamine in large volume of ethanol gives only 77% ee diasteromeric salt enriched in d-threo-ritalinic acid.
U.S. Pat. No. 7,247,730 discloses a process for the preparation of threo-N-Boc-ritalinic acid from the methylphenidate in three steps using crystalline sodium N-Boc-threo-ritalinate as precursor.
US 2011/0130569 discloses a process for the preparation of the d-threo-ritalinic acid. dl-threo-ritalinic acid treated with (+)-dibenzoyl-D-tartaric acid as resolving agent in large volume of solvents mixture of methanol/water to get d-threo-ritalinic acid-dibenzoyl tartaric acid salt. Thus obtained salt treated with 35% hydrochloric acid in mixture of toluene and water, concentrated under vacuum and isolated by treating with acetone. The volume of resolution solvent used herein is quite higher.
Hence, there is a need to provide an industrially viable process for the preparation of d-threo-ritalinic acid salt via its novel salts of intermediate avoiding large volume of solvents at resolution stage resulted in very good purity and yield which further helps in increasing the purity and yield of the final product i.e. dexmethylphenidate hydrochloride.